Various methods and compositions for reducing the NO.sub.x concentration in the effluent from the combustion of a carbonaceous fuel have been proposed. For instance, Arand et al, in U.S. Pat. No. 4,208,386, disclose a method for reducing NO.sub.x in combustion effluents by injecting urea, either as a solid powder or in solution, at effluent temperatures in excess of 1300.degree. F. The preferred urea solutions are those having at least 10 weight percent urea. For operation at temperatures below 1600.degree. F., the use of reducing materials such as paraffinic, olefinic, aromatic and oxygenated hydrocarbons, as well as hydrogen, are requied.
Bowers, in copending and commonly assigned U.S. patent application Ser. No. 906,671, filed Sept. 10, 1986, now U.S. Pat. No. 4,751,065 discloses the use of a solution which comprises urea and hexamethylenetetramine (HMTA) to reduce the NO.sub.x concentration in oxygen-rich effluents having temperatures above 1300.degree. F. Similarly, Bowers, in copending and commonly assigned U.S. patent application Ser. No. 784,828, filed Oct. 4, 1985, now U.S. Pat. No. 4,719,092 discloses a solution comprising urea and an oxygenated hydrocarbon solvent which is disclosed as being effective at reducing NO.sub.x concentrations with reduced ammonia slippage in effluents at temperatures above 1600.degree. F.
In copending and commonly assigned U.S. patent application entitled "Process for Reducing Nitrogen Oxides in an Effluent Using a Hydrocarbon or Hydrogen Peroxide" having Ser. No. 022,799,filed Mar. 6, 1987, Sullivan discloses the use of hydrocarbons to reduce NO.sub.x levels in effluents at low temperatures (i.e., below 1450.degree. F., especially below 1300.degree. F.).
Although the prior art processes for reducing nitrogen oxides concentrations are generally effective, there exists a present need for a process which elicits still further NO.sub.x reductions in an economical and convenient manner.